Purification of brasses and bronzes



Patented July 25, 1950 William F. Tschappat, Pittsburgh, Pa., assignor to The American Metal Company, Limited, New

York, N'. Y., a corporation of New York No Drawing. A plication January 22, 1948, Serial No. 3,830

1 This invention relates to the purification of brasses and bronzes and particularly to the removal of sulfur from such metals in an economicalmanner to produce such metals with a lowered sulfur content. 1 The patent to Hanak 1,837,432, patented December 22, 1931, is known tome. It employs a mixture of metallicsodium and sodium carbonate for purification of copper alloys such as brass. So far as I amaware, this process has never been practiced. It is an expensive process because of the use of an expensive metal, viz,, sodium or other alkali metal, which is an essential constituent of the bath according to Hanak. It has also been heretofore proposed, in accordance with another process, to use: soda ash with coal or charcoal which is added to molten brass and rabbled into the mass. This method. of combining the soda ash; and brass has been found to have three major difficulties: (1) It takes a long time to remove the sulfur; (2) one treatment with: soda ash and reducing agent under this old method usually results in relatively small elimination of sulfur and the method had. to be repeated a number of times, and (3) dueto the length; of time necessary for the soda to be in contact with the brass, the wear-and-tear on the furnace linings is greatly increased. The'process not" only consumes considerable time with con sequent wear-and-tear on the furnacelinings, but itrequires over twice as much labor. For in stance, for handling the same amounts of brass or bronze as given in the examples below, five men were required in the operations of the old process for about 6 to 8 hours, while in accord arise with my process, only two men were re quired for approximately two hours. Also, soda ash alone or with a reducing agent has been used by blowing it under the surface of the molten bath, but with about the same disadvantages as just mentioned.

The principal object of the present invention accordingly is to provide a process for purifying brasses or bronzes which will overcome at least,

some of the disadvantages of the prior processes and which will result in the economical removal of sulfur therefrom.

The invention accordingly comprises the novel processes and steps of processes, specific embed? merits of'whic'h are described h reina ter by w 3 Claims. (CI. 7576) of example and in accordance with which I now prefer to practice the invention.

I have found that the reducing agent, namely, coal or charcoal, can beeliminated and the whole process can be greatly simplified and shortened and sulfur can be removed in one step during the melting-down period by first preparing a molten bath of sodium carbonate and then adding the brass to this bath in solid form. As the brass melts, it trickles through the sodium carbonate and removal of sulfur immediately occurs.

4 In carrying, out my process, I charge from 5 to-15% of an alkali such as sodium carbonate or sodium hydroxide orother alkalies hereinbe low defined into an empty reverberatory furnace, for example, The percentage-of such alkali charged is based on the weight of the brass or bronze to'be treated. Thesodium carbonate or other alkali forms a molten bath. While maintaining the bathabove the melting point of the metal-brass or bronze"-t o.be treated, the said metal is charged into the furnace as rapidly as possible and melted. The metal as it melts drips through the molten bath of alkali and produces a slag containing a large part of sulfur. The sulfur is apparently removed from the metal as a complex compound, mostly a mixture of sodium sulfide and sodium sulfite.

My method is. especially useful in cleaning sulfur. These are useful for blending with other Examp e 1. Three thousand pounds of sodium carbonate wasch arged intofa re've'rberatory furnace and caused to form a liquid bath having a temperature of about ZZOO FL charge of 26,018 pounds" of impurered-brass'in rough cast slabs containmetal before and after treatment is given below,

as well as an analysis of the slag.

Analysis before I Treatment After Treatment Slag Analysis TotaL- 99. 90

2. A larger lot of materials was employed in carrying out this second example, the melt being made in a larger furnace with somewhat faster meltingof the soda ash and metal slags resulting in'a single treatment in the removal of a larger amount of sulfur from the metal treated. Sixty six hundred pounds of sodium carbonate was charged and allowed tobecome liquid and maintained at a temperature'about 400 F., above the melting point of impure red brass. 65,603 pounds y of impure red brass containing sulfur and other ingredients as shown below in slab shapes was charged into the furnace as rapidly aspossible and allowed to melt completely. The red brass,

as before, trickled through the molten'bath of sodium carbonate and the sulfur was removed. The slagwas then removed from the molten bath. The bath was well stirred and, onan'alysis, itwas shown that the sulfur in the original metal, am'ounting'to 50%, had been reduced to .05% sulfur. The analysis of the metal before and after treatment, as well as the slag analysis, is given below v Analysis before Treatment After Treatment Slag Analysis 79.74 Cu 6.58 5. 42 Sn .36 7'. 32 Pb 3. 49 Fe 7.38 2.03 S 6.70

Total 99 90 Total- 99.90

of sodium carbonate and the sulfur was removed.

The slag was then removed from the molten bath. The bath was wellstirred and, on analysis, it was shown that the sulfur in the original metal, amounting to 379%, had been reduced to sulfur. The. analysisof the: metal before and 4 after treatment, as well as the slag analysis, is

given below:

Analysis before Treatment After Treatment Slag Analysis Total 99. 92

Total 99. 92

I In place of sodium carbonate in the above examples, there may be substituted caustic soda NaOH, potassium hydroxide or potassium carbonate. These materials operate in the same manner and in equivalent proportio to give the same result but they are more expe sive than the preferred sodium carbonate and the latter is more easily handled in the furnace.

'Instead of brass, a similar weight of bronze may be substituted in the above examples.

In the appended claims, where the term falkali is used, it is intended to designate sodium carbonate, sodium hydroxide, potassium carbonate or potassium hydroxide.

What I claim is:

1.' A process for removing sulfur from impure brass containing same which'comprises, preparing a molten bath of sodium carbonate in the proportion of about 5 to 15% thereof based on the weight of the impure brass charged and while maintaining such bath above the melting point ofthe brass to be treated, charging such brass in unmelted condition thereinto and rapidly completely melting the brass, allowing the molten'b'r'assto trickle through the molten carbonate to produce a slag containing a large part of the sulfur. 7 2. A process for removing sulphur from impure brass or bronze metal containing same, which comprises preparing a molten alkali bath in the proportion of 5 to 15% of theweight of the metal charge to be purified while maintaining such bath above the melting point of the impure metal to be treated, charging such metal in unmelted condition into said molten bath and rapidly completely melting the brass, and allowing the molten metal to trickle through the molten alkali to produce a slag containing a large part of the sulphur.

3. A process for removing sulphur from impure brass or bronze metal containing same, which comprises preparing'a molten alkali bath in the proportion of 5 to 15% of the weight of the metal charge to be purified while maintaining such bath above the melting point of the impure metal to be treated, charging such metal containing .5% to .6% sulphur in unmelted condition into said molten bath and rapidly completely melting the brass, and allowing the molten metal to trickle through the molten alkali to produce a metal which contains about .1 sulphur or less.

' WILLIAM F. TSCHAPPAT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,921,180 Evans Aug. 8, 1933 1,921,868 .Evans Aug. 8, 1933 1,955,726 Archer et a1 Apr. 24, 193d, 

2. A PROCESS FOR REMOVING SULPHUR FROM IMPURE BRASS OR BRONZE METAL CONTAINING SAME, WHICH COMPRISES PREPARING A MOLTEN ALKALI BATH IN THE PROPORTION OF 5 TO 15% OF THE WEIGHT OF THE METAL CHARGE TO BE PURIFIED WHILE MAINTAINING SUCH BATH ABOVE THE METING POINT OF THE IMPURE METAL TO BE TREATED, CHARGING SUCH METAL IN UNMELTED CONDITION INTO SAID MOLTEN BATH AND RAPIDLY COMPLETELY MELTING THE BRASS, AND ALLOWING THE MOLTEN METAL TO TRICKLE THROUGH THE MOLTEN ALKALI TO PRODUCE A SLAG CONTAINING A LARGE PART OF THE SULPHUR. 